1. FIELD OF THE INVENTION
This invention relates to a process for forming a color image, more specifically, to a process for rapidly obtaining a color image of excellent quality by fixing with a bath having a pH of at least 6.
2. DESCRIPTION OF THE PRIOR ART
It is important in obtaining recorded information promptly to process photographic materials as rapidly as possible, and this is especially so in the case of radiographic materials. Automatic processors are known which attempt to process exposed radiographic materials within the shortest possible time by conducting a photographic material at a fixed rate from one processing unit to another (for example, see U.S. Pat. No. 3,025,779). A method is also known which comprises processing an exposed black-and-white radiographic material by means of such an automatic processor within 3.5 minutes to thereby form an image (for example, see U.S. Pat. No. 3,545,971).
On the other hand, it is known to form color images by irradiating a color photographic material with radioactive rays. According to this technique, a color radiographic image is formed, optionally together with a silver image, on a radiographic material containing at least one color coupler capable of forming a color image upon coupling with an oxidized aromatic primary amine developing agent. When the radiographic material does not contain a coupler, development with a color developer containing a coupler likewise affords a color image together with a silver image. As disclosed, for example, in U.S. Pat. Nos. 3,114,833, 2,644,096, 2,931,904, 3,493,748, 3,695,882, 2,994,610 and 3,734,735, and Japanese Patent Publication (OPI) No. 37,539/72, these color radiographic materials have advantages over black-and-white radiographic materials in that the amount of information retrieval possible is increased, the exposure latitude is high, the amount of information carried is high because of good granularity, and the silver halide content can be maintained low.
In the present invention, the term "radiographic" is not especially limited, and includes X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, and the like; for most purposes, on a commercial scale, radiographic materials are generally exposed to X-rays.
Quinoneimine color images formed by the coupling of oxidized aromatic primary amine developing agents with phenol- or .alpha.-naphthol-type color couplers generally decrease in color density in an acidic fixing bath. Since a partially faded color image regains its color upon oxidation, this decrease in color density does not so much pose a problem where there is a silver bleaching step, for example, in the processing of general color photographic materials. However, the method of forming radiographic color images in which color images are obtained together with a silver image through a series of rapid color development, fixing, rinsing, and drying steps does not include a silver bleaching step because there is no need to eliminate silver and it is desired to obtain the images within as short a period as possible. Accordingly, the decrease of color density in the fixing step is a great defect of this method.